Design and Manufacture of a Gamma Spectroscopy System

Two years ago I joined a small group of students endeavoring to build a Farnsworth Fusor. Six years after the project was initially started, myself and my two compatriots were the first to observe a steady flux of neutrons emanating from the fusor.

I realized the fusor could now be utilized as a neutron source for experiments in nuclear physics, namely neutron activation work. Thus my biggest contribution to the LMU fusion team was the delivery of a successful gamma spectroscopy system which can be employed in future experiments with the fusor.

Detector Design

This gamma spectroscopy system is based upon the phenomena of scintillation. Scintillation is the process where high energy gamma rays are converted to light in the visible spectrum. The number of visible photons generated is proportional to the energy of the incident gamma ray. A NaI:Tl scintillation crystal and 51mm photomultiplier tube were selected to achieve the highest energy resolution whilst staying within the confines of the budget given to me by the LMU Undergraduate Research Opportunity Program.

Once calibrated this system provided 6.8% FWHM energy resolution in the range to be observed.

CAD Modeling and Manufacturing

The PMT and scintillation crystal are both very delicate instruments. I designed a housing module to align and protect the instruments out of 6061 aluminum. The CAD model was build via SolidWorks and the components machined via GibbsCam, CNC mill and expertise of the LMU resident machinist.

Above: CAD model and finished components

Test of PMT and scintillation crystal to verify performance before integration into housing module